In a fixed disc hard disc drive which are common to personal computers, the disc drive actuator and recording heads must be prevented from sudden movements when the disc drive is powered down in order to prevent damage to the disc recording media. This is a particular problem in drives using a voice coil motor; when the disc drive is powered down, there is no force which will prevent the recording heads from moving out of a landing zone and into areas of the recording media where data is stored and hitting the disc surface causing data loss. This is especially true with notebook and portable computers which are frequently moved and jostled.
Initially, the disc drive actuator arm was held in place by a physical lock which prevented movement. The problem with a physical lock is that it can fail in the locked position and prevent any further use of the disc drive until repaired. Also, a physical lock requires its own power source which increases power demand within the disc drive and increases the heat generated by the disc drive. These physical locks were often used for 3.5" disc drives since the drives were very large and could house a large power supply easily.
However, with the introduction of notebook and portable computers, hard disc drives needed to be much smaller, lighter and consume less power. The extra power required by a physical lock could no longer be tolerated and the excess heat generated by a larger power supply could not be adequately dissipated. In addition, since the newer hard disc drives are designed to be lightweight, the addition weight for the power supply needed for a physical lock can not be tolerated. Also, the extra space required by the larger power supply and the physical lock is not desirable.
After physical locks, ramp latches were introduced which did not require an independent power supply and were smaller in size. These ramp latches, however, required a ramp onto which the actuator arm was locked and required a physical lock to lock the actuator arm onto the ramp. Thus, if the physical lock failed, the disc drive would be inoperative until repaired.
After ramp latches, inertial latches were introduced which used the inertia of the latch to offset the inertia of the actuator arm and stop the movement of the actuator arm. These prior art inertial latches, however, were large since the lock itself held the actuator arm steady. In addition, the prior inertial latches were large since the inertia of the latch itself had to be large enough to balance and counteract the huge inertia of a large heavy actuator arm assembly.